Cutaneous exposure to highly reactive and toxic arsenicals such as lewisite, diphenyl chloroarsine, diethyl chloroarsine and diphenyl cyanoarsine may occur accidently or by deliberate release. Acute cutaneous exposures cause severe local blistering and inflammation in distal organs, such as the lung, causing injury and respiratory failure. The pathogenesis of arsenical-induced lung injury is incompletely understood and a search for effective treatment regimens has been a challenge. Using RNA-Seq of lungs obtained from cutaneous exposed arsenical we identified several bromodomain 4 (BRD4) target genes that were altered. BRD4 is a member of the bromo- and extra-terminal (BET) domain family of proteins that on binding to acetylated histones initiates the inflammatory cascade. This proposal focuses on understanding the role of BET proteins and associated inflammatory pathways in cutaneous arsenical-induced acute lung injury (ALI) and delayed lung injury (DLI). Our preliminary data indicates increased BRD4 protein and histone acetylation in lung following cutaneous arsenical exposures. We also demonstrate that JQ1, a BRD4 inhibitor, mitigates lung injury and decreases inflammatory cytokines such as IL-6, following cutaneous exposure to phenyl arsineoxide (PAO; a surrogate arsenical). Therefore, we hypothesize that toxic doses of arsenicals cause acetylation of proteins and subsequent binding to BET proteins, resulting in activation of injury pathways, and that blocking BET signaling or its downstream effectors can mitigate arsenicals-induced lung injury. The proposed studies are divided into three specific aims. Aim 1 will characterize arsenical-induced lung injury in mice following cutaneous exposures to arsenicals. These exposures will be carried out at MRIGlobal, a contract organization specializing in carrying out such exposures. For mechanistic studies and testing of therapies, aim 1 will also develop an in-house PAO model of cutaneous arsenical-induced ALI and an inhalation model of arsenic trioxide (ATO). Studies in Aim 2 will determine mechanisms by which arsenicals cause acute pulmonary toxicity. These in vitro and in vivo studies will be carried out using both warfare-related arsenicals and surrogates of arsenicals in primary lung cells and mice and will identify downstream therapeutic targets and molecules that can mitigate the toxicity induced by these chemicals. These studies will utilize the Drug Development Core in acquiring novel synthetic or FDA- approved molecules to test for therapeutic efficacy. Studies in Aim 3 will determine whether small molecule inhibitors of bromodomain signaling can mitigate arsenical-induced lung injury and associated morbidity. These in vivo mouse studies will initially be carried out using ATO or PAO. Successful candidate molecules, obtained through our Drug Development Core, will then be tested with more potent arsenicals. Results of the proposed research will help identify treatment options for cutaneous arsenical exposure-induced lung injury as well as for other potentially toxic chemicals associated with blistering and inflammation.